Signal isolators are typically used to isolate lower voltage circuits from relatively higher voltage circuits. For example, it is frequently desirable to isolate a group of sensors being operated in a relatively higher voltage range from processing being operated in a lower voltage range.
Transformers and optical systems have been used as signal isolators. Transformers are usually rather bulky devices when compared with other electronic components associated with integrated circuits. Therefore, transformers are provided externally of the integrated circuits with which they are used.
Optical isolation is usually accomplished by modulating the signal emitted by an optical emitting device, such as a light emitting diode, in accordance with the signal being processed. The emitting device used in such a system is positioned so that the radiation it emits strikes a detector. The output of the detector is then transferred to a processing circuit. In systems that use plural optical isolators, it is difficult, without the use of a complicated assembly, to prevent radiation emitted by one emitter device from striking other detectors located. Therefore, only one such detector, and hence only one optical isolation device, is usually used in a single package. Optical isolation has not been integrated with electronic components.
It is known to integrate a magnetic signal isolator on an integrated circuit. A magnetic signal isolator usually involves a magnetic sensor and a strap. The magnetic sensor may comprise one or more magnetoresistors, and the strap may comprise one or more straps. The strap is coupled to the input of the magnetic isolator and generates a magnetic field in response to an input signal. The magnetic sensor senses this magnetic field and produces an output signal as a function of the magnetic field. Accordingly, the strap receives an input signal from a first circuit operating at a first voltage level, and the magnetic sensor responds to the magnetic field by producing an output signal in a second circuit operating at a second voltage level, which may be either lower or higher than the first voltage level.
The magnetic sensors of known magnetic signal isolators unfortunately sense not only the magnetic field generated by the strap, but also external magnetic fields. As a consequence, these external magnetic fields introduce an error into the output signal of the magnetic sensor. The present invention is directed to strap and magnetic sensor arrangement that is substantially immune to external magnetic fields.